Fuel requirements. New engines will require ultra-low sulfur diesel that has no more than 15 parts per million of sulfur. (This fuel has been used since 2006 in on-highway vehicles.)

New engine technology. Changes likely to be most noticeable are in placement and packaging of aftertreatment systems and increased size of air intake systems. Most engines will be electronically controlled (a computer will monitor and adjust fuel and air mixture on a real-time basis), and on-road technology likely will be incorporated in the exhaust system (catalytic converters and/or particulate filters), in place of existing muffler and exhaust systems.

EGR or SCR. Two types of engine technology will be used by manufacturers to meet Tier 4 requirements: exhaust gas recirculation (EGR) or selective catalytic reduction (SCR). EGR is a technique that recirculates a portion of the exhaust gases back into the combustion chamber, lowering the combustion temperature and reducing formation of nitrogen oxides. This system will add additional manifolds and plumbing around the engine. SCR technology, used widely in Europe, uses a special catalyst periodically sprayed into the exhaust stream/muffler system to chemically react with exhaust ­nitrogen oxides and lower tailpipe emissions.

Additional training. Mechanics and technicians will need to be versed in the new technologies. New maintenance and filter cleaning schedules may be needed and some maintenance could involve visits to a service facility or an onsite visit by a service vendor.